U.S. Pat. No. 3,401,876 discloses an automated cell washing centrifuge which utilizes centrifugal force to decant supernatant solution as a final step in a cell washing sequence of steps. With the movable cover in its lowered position, the centrifuge tubes are held in inclined position so that during rotation of the rotor saline may be injected into each of the tubes to suspend and wash the cells and, as rotation continues, to pack the cells so that they form cell buttons in the tubes' lower ends FIGS. 10 and 11). Subsequent rotation with the cover in its raised position results in a decanting of the supernatant liquid from the tubes since, during such decanting step, the tubes are supported in substantially vertical positions (FIG. 14).
Later patents disclose modifications in structure and operation for controlling the angular disposition of the tubes during the wash and decant cycles. Thus, U.S. Pat. No. 3,722,789 discloses a centrifuge in which the weight distribution of the tube holder changes depending on whether rotor rotation is clockwise or counterclockwise; during clockwise rotation the centrifuge tube assumes its inclined position for washing and packing of the cells, whereas during counterclockwise rotation the tube assumes its generally vertical decant position. U.S. Pat. No. 3,951,334 similarly discloses a centrifuge in which the angular orientation of the centrifuge tubes is determined by the direction of rotor rotation, the pivotally-mounted tube holders being allowed to swing outwardly when the rotor (drive shaft) turns in a counterclockwise direction but being blocked by castellations against such outward swinging movement when the rotor moves in a clockwise direction.
In U.S. Pat. No. 3,420,437, a latching system in the form of a vertically movable restraining ring is used to secure the tubes in their generally vertical positions during the decant cycle. Although manual operation of the latching ring is shown, in a commercial version the ring is shifted between its latching and unlatching positions by a solenoid.
The centrifuge disclosed in U.S. Pat. No. 3,712,535 employs an electromagnetic holding device to retain the tubes upright during the decant cycle. The electromagnet is stationary and acts through an air gap to tilt the tube carriers from their normal rest positions into the positions they assume during decantation. Magnetic action is aided by a magnetic soft ring located intermediate between the stationary electromagnet and the tube carriers which is free to rotate with the tube carriers, thereby reducing the air gap.
The cell washing centrifuge of the present invention constitutes an improvement over prior constructions in which tubes are supported in generally vertical positions for decanting purposes and in downwardly and outwardly inclined positions for washing and packing of their cellular contents. An electromagnet rotates along with the tube carriers and is in direct surface engagement with the magnetically-attractable contact plates of those carriers when the carriers are in the vertical positions that they assume not only during a decant operation but also when the centrifuge is at rest. Because of such direct contact and the planar surface engagement between the carriers and the pole faces of the magnet, an electromagnet of relatively small dimensions and mass--factors of importance in view of the rotational mounting of the magnet--provides strong attractive forces for securely locking the carriers in their decant positions when the magnet is energized. The result is a highly efficient washing and decanting centrifuge of relatively simple, durable, and reliable construction.
Each of the tube carriers is composed of two main sections, a tube-holding section or member and a magnet-contacting section or member. The two members are suspended at their upper ends from a support ring which is a coaxial part of the rotor assembly. The respective members are independently suspended from the ring and are adjustably connected to each other at their lower ends for selective adjustment of the angle of the tube-holding member during decantation.
Each tube-holding member is typically formed of sheet metal and is folded to provide an open-topped cavity defined by generally planar upstanding side walls. Two of those side walls constitute outer walls which meet along a line lying in the vertical plane of swinging movement of the carrier and defining the outer limits of the cavity. The included angle at the junction of such planar outer walls falls within the general range of 70.degree. to 170.degree.. When the centrifuge is in operation, a centrifuge tube supported within the cavity engages the inside surfaces of the converging outer walls along two parallel lines of contact. Such spaced lines of contact not only distribute stresses on the fragile (glass) centrifuge tube but also adapt the carrier to receive and operate with centrifuge tubes of different outside diameters. The increased contact area also eliminates a tendency observed for light weight (plastic) centrifuge tubes to creep upwardly during decant.
Other features, advantages, and objects of the invention will become apparent from the specification and drawings.